It is known that conductive high polymer compounds include polyacetylene, polypyrrole, polythiophene etc., and they may be applied to various industrial fields such as storage batteries, electrochromic display devices, photocells or other semiconductor articles due to various electrochemical properties such as conductivity of the compounds.
Particularly, the aromatic heterocyclic polymers such as polypyrrole or polythiophene are prepared by a chemical polymerization, using an oxidant such as ferric chloride, and also by an electrochemical polymerization. Recently, numerous research publications and patents have been made public in this field. But, although the known conductive high polymer compounds have excellent electric properties, when the compounds are used to make goods, the goods are easily breakable due to the low mechanical strength of the compound.
Therefore, it was necessary that conductive polymers be prepared having higher strength as well as the prior properties in order to use them in various fields.
In order to find solutions to the above problems, examples of disclosed methods for preparing conductive high polymer composites with the improved property are summarized as follows.
Firstly, there is a process for improving the working property of a conductive high polymer by using a precursor polymer soluble in a solvent. This process is very difficult and intricate, and has the fault that the conductivity of the high polymer is reduced. [Polymer, 1984, 25, 395]
Secondly, there is a method that is comprised of dispersing a catalyst in the base resin and compounding the dispersed resin with a conductive high polymer compound. For example, Ziegler-Natta catalyst is dispersed in the low density polyethylene and it is compounded with a polyacetylene by polymerizing at temperatures of 100.degree. to 120.degree. C. to obtain a conductive high polymer composite. It is known that while the obtained composite has the excellence of mechanical strength, decreases in the conductivity are observed even though after dopping. [Polym. Commun., 1982, 23, 795]
Thirdly, a method is to use para-toluene sulfonate as the electrolyte used for electrochemical polymerization. In this case, a conductive high polymer compound having the high mechanical strength may be prepared without any change in the conductivity. But, the polyelectrolyte in the composite dissolves out after repetitive red-ox reactions in the solution, resulting in the reweakening of the mechanical strength. Therefore, this method is not applicable where the solution is used such as in the case of a storage battery. [IBM J. Res. Dev., 1983, 27, 342]
Fourthly, it is known that a method is provided to form a composite of polyvinyl chloride and polypyrrole or polythiophene, by using an electrode having a surface coated with polyvinyl chloride layer in the step of the electrochemical polymerization, wherein the monomer such as pyrrole or thiophene swells polyvinyl chloride and then the polymerization reaction is carried out therein. This method may be characterized in which the formed conductive high polymer composite has simultaneously the high mechanical strength and the high electric conductivity [Macromol., 1986, 20, 749]. But, in this method, the addition of a stabilizer etc. is necessary since polyvinyl chloride (which has low oxidation stability), is used, consequently, the obtained high polymer composite is not applicable to semiconductor articles o to materials for storage batteries. In view of the above, if the stabilizer is not used, the properties of the composite ar deteriorated owing to the degradation of polyvinyl chloride.
Therefore, there still exists a need for a conductive high polymer composite having the higher mechanical strength, pliability and excellent working properties with the know probable properties.